Radiation detector for a computed tomography

ABSTRACT

A radiation detector for an X-ray computed tomography apparatus, has a number of detector modules mounted side-by-side, each detector module having a sensor array composed of a number of sensor elements. For simplifying the maintenance of the detector, each detector module contains an electronic memory arrangement for storing data relating to the calibration of each of the sensor elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a radiation detector for an X-raycomputed tomography apparatus, of the type having a number of detectormodules mounted side-by-side, each module having a sensor array composedof a number of sensor elements.

2. Description of the Prior Art

A detector of the above type is disclosed, for example, in German OS 19502 574. The known detector has a number of parallel detector lines thatproceed in the direction of the axis of a subject, for example apatient, to be transirradiated. Each detector line can be implemented asan assembly unit or detector module. A sensor array formed of a numberof sensor elements is thereby accepted on a printed circuit board. Theprinted circuit board is connected via a flexible section to a furtherprinted circuit board on which a plug for connection to a followingevaluation electronics is mounted.

The sensor elements respectively exhibit slightly different properties.In order to avoid image artifacts, it is necessary to calibrate eachsensor element. To that end, calibration tables are produced withspecial measuring devices. The calibration tables contain, for example,information about the temperature behavior, the radiation driftbehavior, the relative signal strength, the persistence behavior, thelocation dependency of the signal strength, the spectral behavior, andmalfunctioning sensor elements.

When a detector module fails, the calibration tables must be producedanew overall after the replacement thereof with a further detectormodule. Due to the considerable time outlay connected therewith and thenecessity of special measuring devices, a malfunctioning detector is,according to conventional procedures, not replaced on site. The entiredetector is replaced by a new detector and the calibration table isdetermined for the new detector by processing in the evaluationelectronics.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate these disadvantagesaccording to the prior art. In particular, it is an object to provide adetector for an x-ray computed tomography apparatus that is as simple aspossible to maintain.

This object is achieved in accordance with the invention, in a detectorof the type described above wherein each detector module contains anelectronic storage arrangement for storing data for the calibration ofeach one of the sensor elements. At a replacement of such a detectormodule, it is no longer required to produce the calibration tables anew.The maintenance of a malfunctioning detector is thus reduced to thesimple replacement of a detector module. This saves time and cost.

The electronic storage arrangement can be an ASIC (application-specificintegrated circuit). Such a component is available at a relatively lowcost.

In an embodiment of the invention, each detector module has atemperature sensor. This makes it possible to calibrate the detectormodule dependent on the current temperature. The measured results thatare supplied are especially precise.

Further, a circuit for digitizing the signals supplied by the sensorarray can be provided. This can be another ASIC. In this case, serialsignals can be communicated directly from the detector module to thefollowing evaluation electronics. The evaluation electronics can becorrespondingly simplified.

The temperature sensor, if used, is formed as preferably a p-nsemiconductor junction, and can be a component of the ASIC serving forstorage or of the further ASIC. Such a temperature sensor thus can bemanufactured in an especially economic way.

The sensor array can be a photo-diode array by a number of photo-diodes.Each sensor element is expediently formed of a photo-diode provided witha scintillator element at the radiation entry side. The storagearrangement is preferably mounted on a printed circuit board thataccepts the photo-diode array. The printed circuit board can beconnected via a flexible section to a further printed circuit board thataccepts a plug. The above features contribute to a compact structure anda simple replaceability of the detector module.

The invention also is directed to an x-ray computed tomography apparatushaving an inventive detector module is claimed.

DESCRIPTION OF THE DRAWINGS

The single FIGURE, is a side view partly in section, of an exemplaryembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detector module of an x-ray computed tomography apparatus is shown ina schematic cross-sectional view. A sensor array referenced 1 overall iscomposed of a photo-diode array 2 that is formed of a number ofphoto-diodes 3. A scintillator element 4 is mounted on each photo-diode3 at the radiation entry side. Together with the scintillator element 4,the photo-diode 3 forms a sensor element. The sensor array formed of anumber of sensor elements is mounted on a first printed circuit board 5.The first printed circuit board 5 is connected to a further printedcircuit board 6 via a flexible section 7. Interconnects are conducted inthe flexible section 7 (not shown). A plug 8 for connection of thedetector module to an evaluation electronics (not shown here) isprovided on the further printed circuit board 6. A number of printedcircuit boards 5 a, 6 a can also cover the flexible section 7 in thefashion of a sandwich structure for reinforcing the detector module.

A first ASIC 9 and a second ASIC 10 are mounted on the printed circuitboard 5. The first ASIC 9 serves the purpose of digitizing the signalssupplied by the sensor array 1. An electronic memory is provided in thesecond ASIC 10. The data for calibration of each of the sensor elementsare stored in this memory. These data particularly include the followinginformation: temperature behavior, radiation drift behavior, relativesignal strength, persistence behavior, location dependency of the signalstrength, spectral behavior, and information about malfunctioning sensorelements.

The digital signals supplied by the first ASIC 9 can be calibrated bymeans of the calibration data deposited in the second ASIC 10 and can beforwarded as serial signals to the following evaluation electronics viathe plug 8.

It has proven especially advantageous to integrate a temperature sensorin the form of a p-n semiconductor junction in the second ASIC 10. Thecalibration can thus ensue dependent on the temperature prevailing atthe detector module. Especially exact measured results are supplied. Theimage resolution can thus be enhanced.

The above self-calibrating detector module is simple and constructed ina compact way. An x-ray computer tomograph having a detector comprisingthe disclosed detector modules can be maintained fast and simply.

Although modifications and changes may be suggested by those skilled inthe art, it is in the intention of the inventor to embody within thepatent warranted hereon all changes and modifications as reasonably andproperly come within the scope of his contribution to the art.

I claim as my invention:
 1. A radiation detector for an X-ray computedtomography apparatus, comprising: a plurality of radiation detectionmodules mounted side-by-side; each radiation detector module comprisinga sensor array formed by a plurality of radiation sensor elements, eachof said sensor elements requiring calibration; and each of said detectormodules containing an electronic memory arrangement in which data forcalibrating each of the sensor elements of that module are stored.
 2. Aradiation detector as claimed in claim 1 wherein said electronic memoryarrangement is an application-specific integrated circuit.
 3. Aradiation detector as claimed in claim 1 wherein each detector modulefurther comprises a temperature sensor.
 4. A radiation detector asclaimed in claim 1 wherein the respective sensor elements of said sensorarray emit analog signals, and wherein each of said radiation detectormodules comprises a digitization circuit, to which said analog signalsare supplied, for digitizing said analog signals.
 5. A radiationdetector as claimed in claim 4 wherein said digitization circuit is anapplication-specific integrated circuit.
 6. A radiation detector asclaimed in claim 1 wherein said application-specific integrated circuitis a first application-specific integrated circuit, and wherein saidradiation detector further comprises a temperature sensor, and whereinsaid sensor elements in said sensor array respectively emit analogsignals, and wherein each of said detector modules further comprises asecond application-specific integrate circuit to which said analogsignals are supplied, for digitizing said analog signals, and whereinsaid temperature sensor is a component of one of said firstapplication-specific integrated circuit or said secondapplication-specific integrated circuit.
 7. A radiation detector asclaimed in claim 6 wherein said temperature sensor is formed as aPN-junction.
 8. A radiation detector as claimed in claim 1 wherein saidsensor array is a photodiode array composed of a plurality ofphotodiodes as said plurality of sensor elements.
 9. A radiationdetector as claimed in claim 1 wherein each of said sensor elements hasa radiation entry side, and wherein each of said sensor elementscomprises a photodiode preceded by a scintillator element disposed atsaid radiation entry side.
 10. A radiation detector as claimed in claim1 wherein said sensor array comprises a photodiode array formed by aplurality of photodiodes as said plurality of sensor elements, andwherein each of said detector modules comprises a printed circuit boardon which said photodiode array is mounted, and wherein said memoryarrangement is also mounted on said printed circuit board.
 11. Aradiation detector as claimed in claim 10 wherein said printed circuitboard is a first printed circuit board, and further comprising a secondprinted circuit board that accepts a plug, and a flexible sectionconnecting said first printed circuit board and said second printedcircuit board.